During the past eight years, major developments have been made in flow systems for rapid cell analysis. The biophysics group of the Los Alamos Scientific Laboratory is one of the few groups that pioneered the development of this instrumentation. This instrumentation has potential applications in biology and medicine. The objective of this proposal is to apply this instrumentation to some of the selected problems in radiobiology related to oncology. The proposed research is aimed to explore the potential application of this instrumentation to cell viability studies after exposure to ionizing radiation or chemotherapeutic drugs, radiobiology studies in rodent tumors, multicellular spheroids and cultured cells, and DNA measurements of spontaneous tumors in dogs to see if there is a correlation between flow data and histopathology.